1. Field of the Invention
The present invention relates to a disk device, a track positioning method, and a method for generating a position error signal which are used in a hard disk drive (HDD) or the like, and particularly to a disk device, a track positioning method, and a method for generating a position error signal in which a magnetic head is positioned at the center of a target track.
2. Description of Related Art
In the hard disk drive (HDD) which is used as an external storage device for information processing systems, more size reduction and higher reliability are demanded. In the conventional hard disk, data tracks are concentrically formed. A reading or writing of information to the magnetic disk is performed after a seek operation, that is, after rotating the magnetic disk and moving the magnetic head substantially radially of the magnetic disk to position the magnetic head at a specific data track. The positioning of the magnetic head at a specific data track is performed by using the magnetic head to respectively read head position identifying information and burst patterns which are prerecorded on the magnetic disk.
FIG. 7 is a figure schematically showing the data areas and the servo areas of a magnetic disk. As shown in FIG. 7, data areas 11 and servo areas 12 are separately formed in a magnetic disk 10, and a magnetic head identifies the position according to the servo data recorded in these servo areas 12, and writes data to the data area at a desired position, or reads it.
FIG. 8 is a figure showing part of the head position identifying information and burst patterns which are recorded on the magnetic disk. In FIG. 8, the magnetic disk rotates along the circumferential direction (the direction of arrow F in FIG. 8), and the magnetic head, not shown, moves along substantially the radial direction of the magnetic disk (the direction of arrow G in FIG. 8). Concentrically formed in the magnetic disk are a plurality of data tracks 20A, 20B, 20C, . . . on which data are recorded. Data tracks are arranged along the circumferential direction, and between the adjacent data tracks, an identifying information recording area 21 and a burst pattern recording area 22 are formed.
The cylinder (CYL) and sector (SEC) position information, which is information for identifying the head position, is contained in the gray code (cyclic binary code) in the identifying information recording area 21. Following the gray code, the burst pattern recording area 22 for providing a fine adjustment signal for the track at the head position is recorded on the disk. By reading these servo data, the magnetic head is positioned at a desired track.
Each data track is previously provided with a track address for identifying itself. Recorded in the identifying information recording area 21 is identifying information of a predetermined number of bits which is representing the track address of the corresponding data track by a gray code. Also recorded in the burst pattern recording area 22 is a plurality of (in FIG. 8, four) burst pattern rows 22A, 22B, 22C, and 22D in which regions having a signal recorded therein (refer to the hatching in FIG. 8) are respectively arranged along the radial direction of the disk.
When the magnetic head is positioned at a desired data track, the track address of a data track which the magnetic head is facing is calculated according to an identifying information read signal, which is outputted from the magnetic head each time the head crosses the identifying information recording area 21.
FIGS. 9(A)-(C) illustrate the use of the gray code in the magnetic disk. FIG. 9(A) illustrates the identifying information, wherein the record length for one-bit data (L in FIG. 9(A)) is predetermined. According to whether the value of each bit of the gray code representing a track address is xe2x80x9c0xe2x80x9d or xe2x80x9c1,xe2x80x9d the recording is made so as to make different the positions of the portions to be magnetized to N or S in a recording region of the length L which is corresponding to each bit.
For instance, if the magnetic head passes the identifying information recording area of a data track N shown in FIG. 9(A), a pulse is generated at a portion magnetized to N or S as shown in FIG. 9(B). Further, if the magnetic head passes the identifying information recording area of a data track N+1 shown in FIG. 9(A), a pulse is generated at a portion magnetized to N or S as shown in FIG. 9(C).
Based on the positions of the pulses of these identifying information read signals, the value of the gray code recorded in the identifying information recording area can be determined, and a track address can be obtained by converting the determined gray code to a binary code. For instance, a gray code (100) is determined from the pulse train of FIG. 9(B), and a binary code (111) is obtained through the conversion of the gray code. Further, a gray code (000) is determined from the pulse train of FIG. 9(C), and a binary code (000) is obtained through a further conversion of this gray code.
If it is determined that the magnetic head has reached the target data track, a position detection signal the level of which linearly varies according to the magnetic head position is generated by analyzing the sum of a plurality of signals obtained by respectively reading the plurality of burst pattern rows in the burst pattern recording area 22. Based on the position detection signal, the magnetic disk is positioned so that the gap of the magnetic head is positioned at the center of the width of the target data track.
As described above, in the sector servo type magnetic disk device, a seek operation is performed for moving the magnetic head onto a target track on the magnetic disk. In the seek operation, there is a speed control in which the servo data prerecorded on the magnetic disk is read out by the magnetic head and the magnetic head is moved to the target track on the magnetic disk according to the servo data that has been read out. There is a further speed control in which, when the magnetic head approaches the target track, the magnetic head is moved to the target track based on the burst pattern read out by the magnetic head. Further, there is a tracking control for positioning the magnetic head at the center of the target track. In addition, also in the tracking control, by moving the magnetic head according to the burst pattern detected by the magnetic head from the target track on the magnetic disk, the magnetic head is positioned at the center of the target track on the magnetic disk. That is, a tracking control is performed in which, if an off-track occurs in the magnetic head, the displacement is corrected to provide on-track control.
However, in the above magnetic disk device, if the magnetic layer formed on the magnetic disk surface peels off or dust is deposited when the magnetic layer is formed, the particular portion easily develops a defect as data is recorded with a high density. If such defect occurs in the recording area of a burst pattern, which is position information for obtaining the positional displacement of the magnetic head from the center of a track, the burst pattern is not correctly read by the magnetic head. As a result, the magnetic head may be determined to be off the center of the target track, when in fact the magnetic head is on the center of the track.
In the above HDD (Hard Disk Drive) using sector servo, if there is a defect in a burst pattern for creating a PES (Position Error Signal) which is the position information of the servo, the servo will perform a wrong correction operation according to the incorrect PES. Accordingly, if there is a defect in a burst pattern, this is handled as a defective sector. This defective sector is reassigned to a different place and written there. However, since the number of sectors that can be reassigned is limited and a seek operation must be performed, a reduction in the performance of the HDD results.
FIG. 10 is a figure for explaining the case in which the servo performs a wrong correction operation according to an incorrect PES if there is a defect in a burst pattern. In FIG. 10, nxe2x88x922, nxe2x88x921, n, n+1, . . . represent servos, and is assumed that there is a defect in a burst pattern at the servo n. Then, at the servo n, the PES is incorrectly made, and as shown in FIG. 10, the PES has a value that is significantly different than the preceding servos nxe2x88x921 and nxe2x88x922. Thus, an off-track operation occurs in the read/write head, and several servo sectors are required to perform an operation for correcting the position to the center of the track, as shown in FIG. 10. In the current HDD, since a plurality of data sectors exists in one servo sector as the storage capacity becomes larger, a large amount defective sectors occur. But as mentioned above, the defective sectors may be reassigned to different places within limits, but since seek operations must be performed, the performance of the HDD degrades.
Conventionally, if there is such a defect in a burst pattern, a technique has been taken in which the PES obtained from that burst pattern is not used, and a dummy PES as if there is no change in speed and position is used to prevent a wrong correction operation from being caused. However, in such conventional method using a dummy PES, the correct position and speed are not known since the PES obtained from the burst pattern having a defect is not used. Thus, a wrong data can be read out, or an off-track data writing can be performed to destroy the data in the adjacent track.
It can be seen then that there is a need for a disk device, a track positioning method, and a method for generating a position error signal, in which a wrong correction operation can be prevented by creating an appropriate PES without using a burst pattern having a defect.
It can also be seen that there is a need for a method that decreases the reassigment of sectors to prevent performance degradation by decreasing defective sectors.
To overcome the limitations in the prior art described above, and to overcome other limitations that will become apparent upon reading and understanding the present specification, the present invention discloses a disk device, a track positioning method, and a method for generating a position error signal in which a magnetic head is positioned at the center of a target track.
The disk device of the present invention is a disk device in which a position error signal is generated using burst patterns read out from a disk in which at least a pair of burst patterns are recorded on each of a plurality of tracks, and a head is positioned at a desired track according to the position error signal, characterized by comprising a defect detector for detecting the defect of a burst pattern read out from the disk, and a PES generator, when a defect is detected in the burst pattern by the defect detector, that generates the position error signal by using a burst pattern other than the burst position having the defect detected.
The disk device of the present invention is a disk drive in which a position error signal is generated using burst patterns read out from a disk in which at least a pair of burst patterns are recorded on each of a plurality of tracks, and a head is positioned at a desired track according to the position error signal, including a defect detector for detecting the defect of a burst pattern read out from the disk, and an amplitude detector for measuring the maximum amplitude value of a burst pattern other than the burst pattern having the defect detected, and a PES generator for generating the position error signal according to the maximum amplitude value when a defect is detected in the burst pattern by the defect detector.
The disk device of the present invention is a disk device in which a position error signal is generated using burst patterns read out from a disk in which at least a pair of burst patterns are recorded on each of a plurality of tracks, and a head is positioned at a desired track according to the position error signal, including a defect detector for detecting the defect of a burst pattern read out from the disk, and an amplitude detector for measuring the maximum amplitude value of the burst pattern pairing with the burst pattern having the defect detected, and a PES generator for generating the position error signal according to the maximum amplitude value when a defect is detected in the burst pattern by the defect detector.
An aspect of the present invention is that, when a defect is detected in the burst pattern by the defect detector, a data value corresponding to the sum data of the burst pattern pair having the defect detected is obtained by measuring the maximum amplitude value of the burst pattern pairing with the burst pattern having the defect detected, and the position error signal is generated according to the maximum amplitude value.
The defect detector may be the one which compares the amplitude of a burst pattern with the amplitude of the corresponding preceding burst pattern, and detects the defect of the burst pattern according to the comparison result. Further, the above maximum amplitude value may be a maximum value obtained when the head passes in the vicinity of the center of the burst pattern.
The above disk device may be the one which further includes a drive for driving the head onto the disk, wherein the maximum amplitude value is measured by causing the head to track the center of the burst pattern.
The position error signal after the detection of the defect of the burst pattern is generated according to the amplitude of a burst pattern other than the burst pattern having the defect detected, and the measured maximum amplitude value.
The track positioning method of the present invention is a track positioning method for generating a position error signal by using a recording medium in which at least a pair of burst patterns are recorded on each of a plurality of tracks, and a burst pattern read out from the recording medium, wherein a head is positioned using the position error signal, including measuring the amplitude of the burst pattern read out from the recording medium, detecting the defect of the burst pattern read out from the recording medium, measuring the maximum amplitude of the burst pattern pairing with the burst pattern having a defect detected when the defect is detected in the burst pattern, and generating a position error signal according to the amplitude and the maximum amplitude of the burst pattern pairing with the burst pattern having the defect detected.
The method for generating a position error signal of the present invention is a method for generating a position error signal by using a first burst pattern and a second burst pattern, including measuring the amplitude of the first burst pattern, determining whether the second burst pattern has a defect, and generating a position error signal from the amplitude of the first burst pattern and the maximum amplitude of the first burst pattern when it is determined that the second burst pattern has a defect.
These and various other advantages and features of novelty which characterize the invention are pointed out with particularity in the claims annexed hereto and form a part hereof. However, for a better understanding of the invention, its advantages, and the objects obtained by its use, reference should be made to the drawings which form a further part hereof, and to accompanying descriptive matter, in which there are illustrated and described specific examples of an apparatus in accordance with the invention.